US5229722A - Nqr-imaging - Google Patents

Nqr-imaging Download PDF

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US5229722A
US5229722A US07/738,593 US73859391A US5229722A US 5229722 A US5229722 A US 5229722A US 73859391 A US73859391 A US 73859391A US 5229722 A US5229722 A US 5229722A
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sample
radio
field
coil
frequency
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Eberhard Rommel
Peter Nickel
Rainer Kimmich
Daniel Pusiol
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Bruker Biospin GmbH
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Broker Analytische Messtechnik GmbH
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/445—MR involving a non-standard magnetic field B0, e.g. of low magnitude as in the earth's magnetic field or in nanoTesla spectroscopy, comprising a polarizing magnetic field for pre-polarisation, B0 with a temporal variation of its magnitude or direction such as field cycling of B0 or rotation of the direction of B0, or spatially inhomogeneous B0 like in fringe-field MR or in stray-field imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/441—Nuclear Quadrupole Resonance [NQR] Spectroscopy and Imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/4804—Spatially selective measurement of temperature or pH

Definitions

  • the invention relates to an imaging method for spectroscopy of nuclear quadrupole resonances (NQR), especially with polycristalline, powdery solid samples whereby an RF field having a pulse duration t p with a base amplitude B 10 constant over the sample length for magnetic excitation of nuclear quadrupole resonances with resonance frequencies ⁇ and of the magnetic moments coupled to the nuclear quadrupole moments is applied to the sample and whereby the NQR signal emitting from the sample is time-dependently detected.
  • NQR nuclear quadrupole resonances
  • Imaging methods for nuclear magnetic resonance spectroscopy have nowadays become a standard technique for the investigation of samples producing liquidlike signals.
  • the principles common to all these techniques is magnetic resonance expressed by the equation
  • ⁇ is the gyromagnetic ratio
  • B 0 the external field of the magnet
  • r ⁇ G the additional encoding field produced by the gradient coils.
  • the present invention relates to a method which is based on the second type of nuclear spin resonance, namely nuclear quadrupole resonance (NQR).
  • NQR nuclear quadrupole resonance
  • the attempt to produce images with NQR signals using the normal magnetic field-gradient encoding procedure can lead to severe problems.
  • a NQR imaging method in which by applying a homogenous magnetic field gradient a further broadening of the quadrupole lines proportionally to the local Zeeman field is produced. At zero field position the line width is at the minimum. The known position-dependence of the line width is then used for imaging in NQR measuring.
  • a disadvantage of this method is that for producing a position-dependent Zeeman field an adequate magnet, normally a high-power radio-frequency (RF) magnetic coil, is necessary. Thereby the whole apparatus is doomed to be relatively big and bulky. Moreover, the sample to be examined has to be smaller than the device, since the sample has to be totally inside the Zeeman field.
  • Another disadvantage of the method is that the position-dependence of the line widths in the magnetic field has to be determined by additional measurements. The recording duration of these additional measuring sequences can be compared with the recording duration of the signals for the actual image reconstruction.
  • the RF field is superimposed by a position-dependent field contribution, preferably varying linearly in a spatial direction x corresponding to a constant gradient G 1 x which yields together with the constant RF field a position-dependent RF field B 1 (x), in that the amplitude including its sign is determined for each resonance frequency ⁇ contained in the detected NQR signal, in that the measurements are carried out at different flip angles ⁇ 3 ⁇ B 1 (x) ⁇ t p of the excited magnetic moment, in that the amplitude values including their signs which depend on the flip angle are subjected to a Fourier transformation and in that finally therefrom the x-dependent density distribution of the observed nuclei is reconstructed.
  • the NQR imaging method in accordance with the invention does without extern homogeneous magnetic fields, since in NQR the quantization direction is determined by the crystalline structure and the bonding circumstances. Moreover, the lines of the NQR substances often have a narrow line width which is advantageous in solid imaging.
  • the method according to the invention does without static magnetic field gradients which in the case of solid materials must have considerable strength.
  • the application of a radio-frequency gradient in the NQR zero field resonance method according to the invention permits the imaging of the position resolved density distribution of quadrupole nuclei.
  • the detected time-dependent NQR signal is subjected to a Fourier transformation in order to determine the amplitudes including their signs which depend on the resonance frequencies.
  • the Fourier transformation usually permits a more convenient evaluation of signals with several frequency contributions.
  • an integration of the amplitudes over the resonance frequencies can be carried out subsequent to the Fourier transformation of the time-dependent NQR signal.
  • the nuclear density distribution is to be determined in the x-direction exclusively.
  • this can also be achieved without previous Fourier transformation reducing the calculating time needed for evaluation in that from the time-dependent NQR signal only the amplitude including its sign at a determined time of the measuring is taken to be further evaluated.
  • the different flip angles ⁇ 3 ⁇ B 1 (x) ⁇ t p are produced by variation of the pulse duration t p .
  • This particularly simple version of the NQR imaging method can be carried out on RF transmitters which are common in trade, without a linearly determinable amplitude being needed.
  • the different flip angles ⁇ 3 ⁇ B 1 (x) ⁇ t p can be produced by variation of the gradient G 1 x or by additional variation of the constant base amplitude B 10 .
  • the excitation bandwidth is not changed, which usually is the case when the pulse duration t p is varied because of the different frequency contributions of pulses with different durations.
  • the production of multi-dimensional NQR images according to the projection/reconstruction method is achieved in a preferred embodiment of the imaging method in accordance with the invention in that the measuring and evaluating steps are repeated at different angle positions of the sample relative to the direction of the applied RF gradient G 1 . For doing so, only one single RF coil is necessary and the total pulse duration per scan, i.e. the time from the beginning of the first pulse to the beginning of the signal recording is shorter than in multi-dimensional methods with sequential irradiation of the RF gradient in different spatial directions.
  • the different angle positions of the sample relative to the direction of the applied RF gradient G 1 can be achieved by rotation of the sample. This only requires a device for mechanical rotation of the sample which, especially with small samples, can be a relatively simple apparatus. Another possibility would be the rotation of the corresponding gradient coil which, however, in most cases requires a comparatively greater effort with respect to the apparatus.
  • the different angle positions of the sample relative to the direction of the applied gradient G 1 can be achieved by rotation of the direction of the applied gradient G 1 , especially by applying a sum gradient G 1 which is produced by superimposing of at least two differently directed gradients.
  • a sum gradient G 1 which is produced by superimposing of at least two differently directed gradients.
  • the RF field irradiated in x direction is sequentially superimposed by gradients G 1 x , G 1 y , G 1 2 which are directed into different, preferably orthogonal spatial directions.
  • This version of the method also permits multi-dimensional imaging by using a multi-dimensional Fourier transformation.
  • the calculating method is simpler than in the above described projection/reconstruction method, which can be decisive especially in mobil devices with compacter minicomputers.
  • the same image focus can be achieved all over the image, whereas in the versions described further above less focus and less contrast have to be accepted in the margin portions.
  • the applied gradients G 1 can vary in the known way over the respective gradient direction.
  • the known position-dependent version of the applied gradient or gradients G 1 can be deconvoluted from the measured signals in the evaluation.
  • the invention also comprises an apparatus for carrying out the method in accordance with the invention having at least one RF transmitter coil arrangement for irradiation of an alternating magnetic field B 1 in x direction with superimposed gradient G 1 in a solid sample for excitation of nuclear quadrupole resonances in the sample and with a thereto coaxial receiver coil arrangement for detection of the nuclear induction signal emitting from the sample, whereby the receiver coil arrangement is RF-decoupled from the transmitter coil arrangement.
  • the receiver coil arrangement does not perturbate the irradiated RF field and on the other hand the overdrive of the receiver electronics is avoided due to the relative strong transmitting pulse.
  • the RF transmitter coil arrangement is an anti-Helmholtz arrangement and the receiver coil arrangement is a solenoid coil.
  • the RF transmitter coil arrangement is an anti-Helmholtz arrangement, whereby the sample is arranged coaxially, but asymmetrically between the two coil parts of the anti-Helmholtz arrangement and the receiver coil arrangement consists of an at least two-part air coil arrangement, one part of the air coil surrounding coaxially the sample and its other part being also arranged coaxially to the anti-Helmholtz arrangement within the anti-Helmholtz in axial distance to the sample in such a way that it just compensates the field produced by the anti-Helmholtz arrangement in the part of the receiver coil arrangement surrounding the sample.
  • a surface coil is provided to serve both as an RF transmitter coil arrangement for irradiating an alternating magnetic field B 1 in x-direction with superimposed gradient G 1 into a solid sample for excitation of nuclear quadrupole resonances in the sample and at the same time also as a receiver coil arrangement for detecting the nuclear induction signal emitting from the sample. It is not possible that the transmitter and receiver coil arrangement perturbate each other, because only one single coil is used. An overdrive of the receiver electronics during the recording of a signal emitting from the sample can be subdued by electronic measures. With this embodiment a particularly compact and simple NQR measuring device is provided which is also especially suitable for local measurements of samples which are considerably bigger than the measuring arrangement itself. Because of the compact design of the arrangement mobile use of the device is also possible.
  • FIG. 1 shows a schematic longitudinal section of the sample and the RF coil arrangement whereby the transmitter coil arrangement is realized by an anti-Helmholtz configuration and the receiver coil arrangement by
  • FIG. 2 shows
  • FIG. 3 a vertical section of a NQR measuring arrangement for temperature measurement
  • FIG. 4 a two-dimensional view of As nuclei density of the sample according to FIG. 3.
  • the method in accordance with the invention is based exclusively on the excitation of nuclear quadrupole resonances so that no Zeeman splitting effects have to be taken into account at all.
  • Zero-field NQR is of particular interest with half-integer spins because then even asymmetric electric field gradients do not complicate the spectra by lifting the degeneracY of the eigenstates.
  • Spectroscopic resolution i.e. for instance in the frequency domain in addition to merely spatial resolution therefore is desirable in any case.
  • the method of the present invention is also based on a flip-angle encoding technique.
  • Non-uniform radio frequency (RF) fields are applied so that the flip angle of an RF pulse depends on the position with respect to the RF field gradients.
  • the RF coils are designed to produce preferably constant field gradients.
  • the phase-encoding variant requires an additional and non-selective 90° RF pulse 90° degrees out of phase to the variable flip angle pulses.
  • phase encoding is not feasible because the transverse magnetization oscillates rather than precesses. The following therefore refers solely to the amplitude encoding variant.
  • the transverse magnetization which induces the free-induction decay can then be written in the form ##EQU1##
  • B 1 half of the amplitude of the RF flux density
  • ⁇ j number density of nuclei with the resonance frequency ⁇ j
  • h Planck's constant
  • ⁇ gyromagnetic ratio
  • k B Boltzmann's constant
  • T absolute temperature
  • ⁇ j second moment of the j th resonance line.
  • the angle ⁇ corresponds to the "flip angle" in NMR rotating frame zeugmatography.
  • Amplitude encoding by flip angle variation modulates the magnetization reached after the RF pulse duration t p .
  • the RF field B 1 (x) may be analyzed in a uniform contribution B 10 and a contribution from the RF gradient G 1 . Analogous to eqn. [1], we have ##EQU2##
  • the spatial resolution is determined by the number of steps incrementing the pulse duration t p .
  • the NQR methods are restricted to solid samples, and there is a much simpler way to get access to the other spatial direction, namely the projection/reconstruction procedure.
  • a set of projections on directions varied by small angles step by step is produced by rotating the object relative to the direction of the RF gradient.
  • a method taken from the rotating frame zeugmatography procedure is performed as described above.
  • the increment angle is another quantity determining the spatial resolution.
  • the reconstruction of an image from the recorded data sets is then a standard procedure.
  • HgCl 2 had a purity specification of 99.999%.
  • the spectrometer was tuned to 35 Cl NQR.
  • the isotope 35 Cl has a spin I32 3/2 and a natural abundance of 75.5%.
  • the two 35 Cl atoms are located at different lattice sites and therefore have different NQR frequencies of 22.230 MHz and 22.050 MHz at 30° C. It is important that heating of the samples by irradiation of the RF is avoided carefully, because the resonance frequencies are strongly temperature dependent.
  • the NQR spectrometer implied the following commercial components: modulator and 1.1 kW transmitter (Bruker SXP), synthesizer (PTS 500), preamplifier (Doty LN-2M) supplemented by three serial amplifiers (Avantek GPD 404), personal computer (HP RS/25C), pulse programmer board (SMIS PP2000), bus system (National Instruments GPIB-PC), active filter (Rockland 442), digital oscilloscope (Tektronix 2220).
  • Quad-receiver, probehead and spectrometer software were home-made. Quarter- and half-wave lines with back-to-back diode arrangements were used in the transmitter/probehead system.
  • the RF gradients were produced by the aid of an anti-Helmholtz coil 2 (FIG. 1).
  • the sample 1 in FIG. 1 is placed in one half of the coil arrangement.
  • the receiver coil arrangement is a solenoid coil 3 coaxial to the anti-Helmholtz coils 2 of the transmitter coil arrangement.
  • it can, as shown in FIG. 1b, also consist of two or more air coil parts, whereby an air coil part 3' surrounds the sample and another air coil part 3" in the vicinity of the part of the anti-Helmholtz arrangement which is turned away from the sample is provided for field compensation.
  • the two air coil parts 3' and 3" are electrically connected in such a way that in the two coil parts the current flows in the same sense around the coil axis.
  • the sample in the shown experiment has a diameter of 8.5 mm
  • the anti-Helmholtz configuration 2 has a diameter of 20 mm
  • a coil distance of 17.3 mm and a number of windings 2 ⁇ 8.
  • the solenoid coil 3 in FIG. 3a has a diameter of 14.5 mm, a length of 21 mm and 25 windings.
  • the duration of a 90° pulse at the position with the highest B 1 field was measured with a probe sample to be about 32 ⁇ s.
  • the increment interval ⁇ t p of the RF pulse duration was chosen to be 8 ⁇ s. Higher values led to excessively long pulses so that their bandwidth was not sufficient anymore.
  • FIG. 2a shows a schematic cross section of an HgCl 2 object with HgCl 2 sections 4 and PFTE spacers 5.
  • the corresponding NQR signal amplitude as function of the pulse duration t p is shown in FIG. 2b.
  • FIG. 2c shows, assuming a constant gradient T 1 , a reconstructed X-profile as well as the corresponding mirror profile.
  • FIG. 2d shows a reconstructed profile as in FIG. 2c, which however is corrected in view of the deviations from a constant gradient G 1 . This profile is reconstructed by inserting eqn. [10] in eqn. [9].
  • the sample configuration consisted of two layers 7 of As 2 O 3 powder with a width of 0.8 mm and with a distance of 2 mm fixed by a teflon spacer 5 (FIG. 3).
  • the upper end of the sample configuration was cooled to 6° C. by a liquid cooling design consisting of a refrigerant inflow 11, a cooling bath 12, a refrigerant discharge 13 and a seal 14, the lower end of the configuration had room temperature (about 20° C).
  • the arrow 10 shows the direction of the corresponding temperature gradient.
  • the layers 7 as well as the teflon spacer 5 had a diameter of 13.7 mm, the layers 7 a width of 0.8 mm each and the teflon spacer 5 a width of 2 mm.
  • the NQR imaging experiment was carried out analogous to the one described before. The only difference was that now not only one single frequency point, but for each frequency point in the resonance spectrum an own profile was reconstructed. Thus, on the whole, by a two-dimensional Fourier transformation a two-dimensional image was calculated which shows in vertical direction the position-dependent and in the horizontal direction the frequency and thus in this case the temperature-dependent density distribution of the Arsenic nuclei.
  • FIG. 4 shows clearly that the two sample parts have a different resonance frequency corresponding to a different temperature.
  • step width for the pulse duration t p 3 ⁇ s were used, 64 steps were performed.
  • the duration of a 90° C. pulse for a sample within the coil was about 4 ⁇ s.
  • the spatial resolution is 0.5 mm
  • the frequency resolution is 4 kHz corresponding to a temperature interval of 1.4° C.
  • NQR imaging refers to solid objects where quadrupole splitting is not quenched by rapid reorientations. Nevertheless the technique is not susceptible to the disadvantages of solid-state NMR imaging: Because the direction of quantization is given by the molecular or crystal frame rather than by the direction of an externally applied field, the resonance lines are relatively narrow (3 to 5 kHz in the present case), and they are reasonably well resolved.
  • the technique described above is suitable to produce spin density (" ⁇ ") images. Modifications of the procedure leading to images more or less weighted by the relaxation times are also possible.
  • the present NQR imaging method additionally implies the full spectroscopic information, i.e. eg. the information from the frequency domain in addition to the mere spatial resolution, because no readout gradient is applied.
  • the NQR imaging in accordance with the invention is also sensitive to pressure, stress and temperature as well as gradients or generally any functions of these parameters.

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  • High Energy & Nuclear Physics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
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Cited By (18)

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US5309101A (en) * 1993-01-08 1994-05-03 General Electric Company Magnetic resonance imaging in an inhomogeneous magnetic field
US5500591A (en) * 1991-05-02 1996-03-19 British Technology Group Ltd. Methods and apparatus for detecting substances containing nuclei of a first and second kind
US5583437A (en) * 1991-04-02 1996-12-10 British Technology Group Limited Method of and apparatus for NQR testing selected nuclei with reduced dependence on a given environmental parameter
WO1998009178A3 (en) * 1996-08-28 1998-04-16 British Tech Group Method of and apparatus for nuclear quadrupole resonance testing a sample
US5804967A (en) * 1996-11-15 1998-09-08 The United States Of America As Represented By The Secretary Of The Navy Apparatus and method for generating short pulses for NMR and NQR processing
US5886525A (en) * 1997-03-17 1999-03-23 The United States Of America As Represented By The Secretary Of The Navy Apparatus and method for performing NMR spectroscopy on solid sample by rotation
RU2147743C1 (ru) * 1998-10-12 2000-04-20 Пермский государственный университет Способ наблюдения сигналов квадрупольного спинового эха
RU2148817C1 (ru) * 1999-05-12 2000-05-10 Пермский государственный университет Способ наблюдения сигналов квадрупольного спинового эха
RU2151386C1 (ru) * 1999-05-12 2000-06-20 Пермский государственный университет Способ наблюдения сигналов квадрупольного спинового эха
RU2171981C1 (ru) * 2000-12-14 2001-08-10 Пермский государственный университет Способ наблюдения сигналов квадрупольного спинового эха
RU2184368C1 (ru) * 2000-11-20 2002-06-27 Пермский государственный университет Способ наблюдения сигналов квадрупольного спинового эха
RU2187796C2 (ru) * 2000-08-21 2002-08-20 Витюк Борис Яковлевич Способ определения кислотного числа растительных масел
US6674282B2 (en) * 2001-04-09 2004-01-06 The Regents Of The University Of California Method and apparatus for high resolution ex-situ NMR spectroscopy
US20050057251A1 (en) * 2003-09-12 2005-03-17 Suits Bryan H. Radiofrequency surface detection coil
RU2251689C1 (ru) * 2003-10-10 2005-05-10 Кубанский государственный технологический университет Способ определения кислотного числа темноокрашенного растительного масла
US20050202570A1 (en) * 2003-06-11 2005-09-15 Pusiol Daniel J. Method, sensor elements and arrangement for the detection and/or analysis of compounds simultaneously exhibiting nuclear quadrupolar resonance and nuclear magnetic resonance, or double nuclear quadrupolar resonance
US20080018332A1 (en) * 2004-01-07 2008-01-24 David Lieblich Method and apparatus for detection of quadrupole nuclei in motion relative to the search region
CN107389718A (zh) * 2017-06-06 2017-11-24 浙江大学 一种基于核磁共振成像技术的大白菜根肿病早期快速无损检测装置

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GB9325500D0 (en) * 1993-12-14 1994-09-21 British Tech Group Method of and apparatus for detection, and method of configuring such apparatus
WO1996010193A1 (en) * 1994-09-29 1996-04-04 British Technology Group Limited Method of nuclear quadrupole resonance testing and method of configuring apparatus for nuclear quadrupole resonance testing
RU2161300C2 (ru) * 1999-02-15 2000-12-27 Балтийская государственная академия рыбопромыслового флота Способ идентификации и устройство для обнаружения наркотических и взрывчатых веществ

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Cited By (26)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5583437A (en) * 1991-04-02 1996-12-10 British Technology Group Limited Method of and apparatus for NQR testing selected nuclei with reduced dependence on a given environmental parameter
US5500591A (en) * 1991-05-02 1996-03-19 British Technology Group Ltd. Methods and apparatus for detecting substances containing nuclei of a first and second kind
US5309101A (en) * 1993-01-08 1994-05-03 General Electric Company Magnetic resonance imaging in an inhomogeneous magnetic field
US6566873B1 (en) 1996-08-28 2003-05-20 Btg International Limited Method of and apparatus for nuclear quadrupole resonance testing a sample
WO1998009178A3 (en) * 1996-08-28 1998-04-16 British Tech Group Method of and apparatus for nuclear quadrupole resonance testing a sample
US20060273786A1 (en) * 1996-08-28 2006-12-07 Btg International Limited Method of and apparatus for nuclear quadrupole resonance testing a sample
US7109705B2 (en) * 1996-08-28 2006-09-19 Btg International Limited Method of and apparatus for nuclear quadrupole resonance testing a sample
US20050073306A1 (en) * 1996-08-28 2005-04-07 Smith John A. S. Method of and apparatus for nuclear quadrupole resonance testing a sample
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US5804967A (en) * 1996-11-15 1998-09-08 The United States Of America As Represented By The Secretary Of The Navy Apparatus and method for generating short pulses for NMR and NQR processing
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GB2246636A (en) 1992-02-05
DE4024834C2 (enrdf_load_stackoverflow) 1993-02-18

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